Medical devices such as stents, stent grafts, and vena cava filters are often utilized in combination with a delivery device for placement at a desired location within the body. A medical prosthesis such as a stent, for example, may be loaded onto a stent delivery device such as a balloon catheter and then introduced into the lumen of a body vessel in a configuration having a reduced diameter. Once delivered to a target location within the body, the stent may then be expanded to an enlarged configuration within the vessel to support and reinforce the vessel wall while maintaining the vessel in an open, unobstructed condition. In some medical procedures such as a percutaneous transluminal coronary angioplasty (PTCA), for example, the stent may be deployed and expanded within a vessel adjacent to the location where a lesion has been removed to prevent restenosis or prolapse of the vessel at that region. The stent may be either self-expanding, or alternatively, may be manually expanded by the inflation of a balloon on the delivery device.
Inflation expandable stents are typically secured to the balloon catheter in a reduced diameter configuration or profile prior to their use. In some techniques, for example, the stents are loaded onto the balloon and then inserted into a crimping device which applies an inwardly directed radial force to the stent. In some techniques, the balloon may be heated to a temperature above the glass transition temperature of the balloon material, causing the balloon material to flow and attach or mold to the stent material. In some embodiments, an adhesive material having a melt point below that of the balloon material may also be used in some cases to further adhere the stent to the outer surface of the balloon.
The coating of stents is often performed in a separate step prior to being crimped onto the balloon catheter. In some techniques, for example, the entire surface of the stent may be coated by placing the stent in a dip bath containing a drug coating material such as Rapamycin or Heparin. Once coated, the stent is then crimped onto the balloon catheter in a later step using a combination of pressure and heat. In some cases, the application of pressure to the stent during the crimping process may interfere with the drug coating material. The loading of the stent onto the balloon catheter may result in frictional forces exerted on the stent that can cause damage to the underlying coating on the stent, in some cases resulting in chipping of the drug coating. The application of heat to the stent may also cause changes in the chemical composition of the drug coating material and may create thermal cracks in the coating, limiting the types of drug coatings that can be used. Accordingly, there is a need for new apparatuses and methods for coating and crimping medical devices onto delivery devices.